The importance of catchment vegetation alkalinity, phosphorus burial and macrophytes as revealed by a recent paleolimnological study in a soft water lake

The land use within a catchment maymarkedly affect the environmental conditions in a lake and the storage capabilityof its sediments. This study investigated howchanges in the dominant catchment vegetation (fromlocal standsof deciduous trees over extensive heathland with some agriculture tomainly coniferous forest) occurring during thelast ca. 200 years were reflected in the sediments of a soft water lake and how these changes influenced the lakeecosystem. Pollen, macrofossils, metals, different phosphorus (P) forms, organic matter, carbon and nitrogen contentswere determined in short sediment cores. This novel combination of proxies revealed that 1) the reductionof deciduous trees in thewatershed seemingly reduced the calcium(Ca) supply to the lake and thereby its bufferingcapacity. This development was accompanied by decreased abundances of Ca-dependent species and subsequentincreases in acidophilic species. 2) The sedimentary contents of organic matter, non-reactive P and humic-boundP were evidently higher in sediments deposited during the time when deciduous trees were abundant, which isprobably linked to a stabilising effect by Ca. 3) An erosion event clearly reduced the amounts of macrofossils ofisoetid species and characeans, indicating a reduction in their maximum distribution depth because of lowerwater transparency. Overall, the results of our paleolimnological study are of importance within lake managementby convincingly showing how land use changes may (irreversibly) affect environmental conditions and speciescomposition in soft water lakes and the storage of organic matter and P in their sediments